Further to Dave's piece about looking for leaf-mines, it might also be worth while pointing out that they eventually emerge from the mine, so you may be able to see the adult. If they overwinter in the mine or as pupae which have left the mine it is tricky to successfully rear them and quite a bit of effort and thought has to go into it. Even then you may discover just how many are parasitized or otherwise ill and will never make it.
However, some hatch out before winter and Phyllocnistis species are an example of this. I found two mines of P saligna last week and one emerged immediately:
So, if you want to see this rarely spotted, tiny moth, the best way would probably be to search narrow-leaved Willows for the rather obscure mines, now. After emergence they disappear into hibernation, tucked away somewhere.